Examples

So too of reasonings, whether by syllogism, or induction: for both teach through what is previously known, the former assuming the premisses as from wise men, the latter proving universals from the evidentness of the particulars.

And they are legion: other minds, external world, any scientific conclusion in any science (this is why Newton famously insisted that we should not make hypotheses - by 'hypothesis' he meant precisely this sort of 'for all we know' postulation of possible hidden causes in order to pre-empt our conclusions from the evidence), the appearance of evidentness in mathematics (because 'for all we know' there might be some hidden cause making it only seem to be the case that 2+2=4), you name it.